Since September 2018, all new cars have had their fuel consumption measured using the new, official EU test procedure called the WLTP (Worldwide Harmonised Light Vehicle Test Procedure).

You may not be familiar with the WLTP or the NEDC (New European Driving Cycle), the test it replaced, but this marks an important shift aimed at providing more realistic and achievable fuel consumption figures for new vehicles.

Over time, the gap between real-world fuel economy and the official figures quoted by manufacturers has widened.

In 2001, the average difference was around 8%, but by 2014, it had grown to as much as 40%.

Although some discrepancy is expected – since no lab test can perfectly reflect the variety of driving styles, road conditions, and weather – the gap became so large that manufacturers faced criticism for misleading claims.

Ironically, cars marketed as the most economical often had the widest gap between their official and real-world fuel efficiency. This means official figures couldn’t always be trusted, even as a comparison tool.

 

Official Tests

Before being sold, new car models must pass various safety and environmental ‘type approval’ tests.

• One of these tests measures official fuel consumption and CO2 emissions.
• During the test, the car is ‘driven’ on a rolling road following a predefined cycle.
• Manufacturers must publish these official fuel consumption figures and cannot advertise alternative results.

Official CO2 figures are used to calculate car tax, company car tax, and to track progress toward fleet-wide CO2 reduction targets.

CO2 Reduction Targets

EU nations must meet stringent fleet average CO2 emission targets – 130g/km by 2015 and 95g/km by 2020. Heavier vehicles are allowed higher emissions, balanced by lighter vehicles with lower outputs.

Manufacturers are financially motivated, as failing to meet CO2 targets results in hefty fines.

How the Old Test Worked

Prior to September 2018, most vehicles followed the NEDC (New European Driving Cycle), a laboratory rolling road test first developed in the 1970s. It included two segments:

• Urban – A cold start followed by 2.5 miles at an average of 12 mph, briefly reaching 31 mph.
• Extra-urban – Directly after the urban segment, covering 4.3 miles at an average of 39 mph.
• Three figures were calculated: urban, extra-urban, and a ‘combined’ figure weighted from the two.

Issues with the NEDC Test

The NEDC test cycle became outdated and failed to reflect modern driving habits or vehicle performance.

• The test was short and primarily involved low speeds and engine loads.
• The car rarely reached motorway speeds.
• Key electrical systems (air conditioning, lights, etc.) were switched off.
• Manufacturers could exploit test flexibilities to lower consumption figures.
• Testing was conducted at 20–30°C – warmer than typical driving conditions.
• Passenger weight and other loads were not factored in.

The New Test (from September 2018)

The WLTP replaced the NEDC as the official fuel consumption and CO2 measurement for all new cars from 1 September 2018. It had already been applied to new models from 1 September 2017.

The goal is to produce results that better reflect real-world driving, though no test can fully account for variations in style, traffic, or weather.

The WLTP test runs longer, covers more distance, reaches higher speeds, and involves more dynamic driving phases, including low (city), medium, high, and extra-high (motorway) speeds. Fuel consumption figures are published for each phase, along with an overall figure.

From 1 January 2019, all official fuel consumption figures for new vehicles are based on the WLTP.

Vehicle Excise Duty (VED) and company car tax for new cars still reference CO2 figures from either NEDC tests or ‘NEDC equivalent’ values derived from the WLTP until 6 April 2020.

Toxic Emissions in Real Driving

European regulations require that toxic emissions are minimized not only in lab tests but also in real-world conditions throughout the vehicle’s lifespan.

This is where Real Driving Emissions (RDE) tests come into play.

RDE uses Portable Emissions Measurement Systems (PEMS) to track NOx, CO, and particulate levels while vehicles are driven on public roads.

RDE applies to all new models from September 2017 and to all vehicles from September 2019.

Unlike lab tests, RDE is more demanding, allowing higher emissions limits through a ‘conformity factor’ in two stages:

• Step 1: From September 2017, RDE emissions can be up to 2.1 times higher than WLTP limits.
• Step 2: From January 2020 (new models) and January 2021 (all new cars), emissions can be up to 1.5 times higher.

Buying a New Car

From 1 January 2019, quoted fuel consumption figures for new cars are based on the WLTP, offering a more accurate estimate. Figures for low, medium, high, and extra-high speeds will give insight into fuel efficiency for different driving conditions.

For used cars, the gap between official and real-world figures varies by age – around 10% for mid-2000s cars, and 25% or more for mid-2010s models.

Real-World Fuel Economy Resources

• Real MPG (Honest John) – Over 100,000 user-reported figures show cars typically achieve 84% of the official rating.
• Spritmonitor.de – A German database where users track fuel economy through fuel purchases and mileage (figures in litres/100 km).